1. Field of the Invention
The present invention relates to a porous water-treating material and a process for producing the same. More particularly, the present invention relates to a water-treating material useful for eliminating organic and/or inorganic substances dispersed, emulsified, and/or dissolved in water in an excellent efficiency and a process for producing the same.
2. Description of the Related Art
Various methods are known for treating waste-water containing organic substances, especially, oily substances. For example, various mechanical water-treating methods are known, such as natural flotation, forced flotation, filtration, and centrifugal gravitational separation methods; electromagnetic methods, for instance, ultrasonic, electrolytic, and electrophoresis separation methods; other physical or chemical methods, for instance, adsorption, absorption, ion-exchange, and coagulation separation methods; and biological separation methods utilizing microorganisms.
Among the above-mentioned methods, a variety of adsorbing materials have been attempted in connection with the absorption method, which features relatively simple and stable operation. However, no adsorbing material has yet been found that is effective for treating finely dispersed and emulsified oily substances. With regard to the absorbing materials which have now been attempted, for example, the hydrophobic synthetic fibers or fine synthetic resin structures are mainly used for eliminating floating oily substances or coarsely dispersed oily substances in water. Activated carbon in the form of granules is effective to some extent for eliminating finely dispersed oily substances. The activated carbon, however, absorbs the oily substances in very small amounts and is less effective for eliminating the emulsified oily substances.
In order that the water-treating material exhibit a high capability of eliminating the oily substances from water, it is necessary that the water-treating material have a large specific surface area which results in a high contact efficiency of the water-treating material with the oily substances in water. For example, it is preferable that the water-treating material be of a porous structure.
For the water-treating porous material, attempts have been made to use a resinous matrix material consisting essentially of an organic polymer material alone or a blend of a organic polymer material with an inorganic filler. This type of porous water-treating material is usually prepared by allowing a plate or large mass made of a resinous mixture of the resinous matrix material with a blowing agent to foam and by dividing the resultant porous plate or mass into pieces having a desired size. The dividing step is carried out by a cutting or pulverizing operation.
The pulverizing operation should be followed by a screening operation to collect the porous material particles having the desired size. This, however, complicates the process for producing the water-treating material. Also, the resultant water-treating material particles are distributed over a wide range of size. Therefore, it is difficult to collect particles having the desired size at a high efficiency.
Another disadvantage of the conventional water-treating material is in that it is effective only for eliminating the oily substances floating on the water surface and particles of the oily substances having a relatively large size dispersed in water. That is, a water-treating material effective for eliminating fine particles of the oily substances dispersed or emulsified in water has not yet been formed.
Usually, colloidal particles of the oily substances stably dispersed in water or fine droplet particles of the oily substances or a hydrophobic polymeric substances have negative charges in the surface layer of the particles. The stability of the particles of the oily substances is dependent upon the size of the particles and the amount of the electric charges. Therefore, it is necessary that the water-treating material be capable of neutralizing the negative charges and of the destabilizing the particles of the oily substances. That is, it is preferable that the water-treating material be capable of having charges opposite to those of the particles of the oily substances and of absorbing the oily substance particles therewith. Further, it is preferable that the water treating material include an organic polymer material capable of absorbing or holding the oily substances therewith and, more preferably, that the water-treating material be porous and have a large surface area.
Usually, the process for eliminating the colloidal or fine particles of the oily substances dispersed or emulsified in water is carried out by using a column filled with a water-treating material. In this process, it is preferable that the water-treating material be in the form of grains, granules, or pellets. Also, it is preferable that the distribution in size of the grains be in a narrow range and the grains be capable of precipitating in water.
Furthermore, it is preferable that the small vacant spaces formed between the grains in the water-treating materials be resistant to closure by the solid substances in water so that the pressure of the water flowing through the column filled by the water-treating material can be maintained substantially constant and that, if the small vacant spaces are closed, the solid substances can be easily removed from the water-treating material by washing it with water.
Still furthermore, it is preferable that the water-treating material have a high mechanical strength and hardness.